This application is based upon Japanese Patent Application No. 2000-343663 filed on Nov. 10, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to manufacturing method for producing single-crystal silicon carbide that has low defects and high quality, and apparatus suitable for the same.
2. Related Art
Silicon carbide (hereinafter, SiC) has been developed as a semiconductor substrate for a power device because SiC has characteristics such as withstanding high voltage and high electron mobility. Generally, the single-crystal SiC is produced by single crystal growth method called sublimation (the Modified Lely Method).
In the Modified Lely Method, silicon carbide source material is held in a graphite crucible, and a seed crystal is held in the graphite crucible so as to face the source material. In this state, the source material is heated up to about 2200 to 2400xc2x0 C. to generate sublimed gas while temperature of the seed crystal is kept to be lower than that of the source material by several ten to several hundred xc2x0 C., whereby the sublimed gas is recrystallized at a growth surface of the seed crystal to form SiC single crystals.
However, there is limit to growth in the Modified Lely Method as the source material decreases in accordance with growth of the SiC single crystals. Although new source material can be added, SiC is sublimed at a rate in which Si to C is more than 1, so that concentration of the sublimed gas vacillates when the new source material is added in the middle of growth, thereby preventing crystals from growing in high quality successively.
On the other hand, epitaxial growth method of SiC single crystals by CVD (Chemical vapor Deposition) is disclosed in JP-A-11-508531 (U.S. Pat. No. 6,039,812). FIG. 3 shows a schematic cross sectional view of an apparatus for the epitaxial growth method described in the above-mentioned publication. As shown in FIG. 3, a susceptor 2 as a crucible disposed approximately at a center of a case 1 having a cylinder shape. The susceptor 2 is composed of high-purity graphite or the like. SiC single crystal substrate is disposed on an inner surface of the susceptor 2 at an upper side thereof as a seed crystal for epitaxial growth. Heater 4 is provided at an outside portion of the case 1 where the susceptor 2 is disposed inside of the case 1 to heat gases inside of the susceptor 2.
Space surrounding the susceptor 2 is filled with thermal insulator 5 composed of porous graphite. An inlet conduit 6 having a funnel shape is located under a bottom of the susceptor 2 that is formed by the thermal insulator 5. A supplying portion 7 is located at a bottom of the case 1 to supply a mixture gas while outlet conduits 8 are disposed at a top of the susceptor 2 to exhaust the mixture gas. Moreover, a conduit 9 is disposed at upper side of the case 1 that communicates outside of the case 1.
In this apparatus constituted described above, the mixture gas supplied by the supplying portion 7 is transferred to the susceptor 2 through the inlet conduit 6 formed by the thermal insulator 5, and the mixture gas is heated by the heater 4 and epitaxial growth occurs on the seed crystal 3 as silicon carbide single crystals. Remaining mixture gas is exhausted through the outlet conduits 8 disposed at the top of the susceptor 2, and the conduit 9 disposed at the upper side of the case 1.
However, as shown in FIG. 3, in an invention as described in JP-A-11-508531, difference in size between the inflow port 6 and the outflow port (the outlet conduit at the upper side of the susceptor 2) 8 for the mixture gas at the susceptor 2 is small. Therefore, there is little difference in pressure between the inside of the susceptor 2 and the outside of the susceptor 2. In such a situation where the difference in pressure does not exist, the mixture gas introduced inside the susceptor 2 tends not to remain there and to be exhausted from the outflow port 8.
Therefore, the mixture gas does not contribute to the growth of SiC single crystals sufficiently and is exhausted. Thus, plenty of the mixture gas must be introduced into the susceptor 2. As a result, yield is small, which corresponds to a rate of mol of SiC single crystals to mol of Si and C in the mixture gas introduced into the susceptor 2.
The present invention has been made in view of the above-mentioned problem, and an object thereof is to provide a manufacturing method of silicon carbide single crystals that is improved in yield, and an apparatus for the same.
The present invention has been made in view of the above problems. An object of the present invention is to provide a manufacturing method for producing silicon carbide single crystals, by which yield of silicon carbide single crystals is improved, and a manufacturing apparatus of the same.
According to a first aspect of the present invention, a silicon carbide single crystal substrate is disposed in a crucible, and a gas containing Si and a gas containing C are introduced into the crucible, whereby silicon carbide single crystals grow on the silicon carbide single crystal substrate. Specially, the method is characterized in that pressure in a growth room, in which the silicon carbide single crystals grow on the silicon carbide single crystal substrate, is set bigger than that after exhausted from the growth room.
According to a second aspect of the present invention, after the mixture gas is introduced into the crucible, the mixture gas is returned in an opposite direction with respect to an introduced direction of the mixture gas, and then the mixture gas is transferred to the introduced direction thereof.
According to a third aspect of the present invention, conductance in introducing the mixture gas into the crucible is made bigger than that in exhausting the mixture gas from the crucible.
Preferably, sectional area of the inflow port through which the mixture gas is introduced into the crucible is set bigger than that of the outflow port from which the mixture gas is exhausted.
Preferably, said crucible has a first member, a second member having a wall portion at a bottom thereof. The wall has an opening. The first member is disposed inside the second member with gap formed therebetween. The silicon carbide single crystal substrate is disposed inside of the crucible at an opposite side with respect to the wall. The mixture gas introduced through the opening reaches the silicon carbide single crystal substrate, then, passes through an interval formed between a tip portion of the first member and the wall portion, and then, is exhausted outside of the crucible through the gap formed between an inner wall of the second member and an outer wall of the first member.
Thus, the apparatus, which preferably performs the manufacturing method of silicon carbide single crystals described in the second aspect of the present invention, can be provided.
Moreover, the crucible has a structure by which conductance in introducing the mixture gas into the crucible is made bigger than that in exhausting the mixture gas from the crucible.
Thus, residence time of the mixture gas in the crucible can be lengthened, whereby a lot of components in the mixture gas can contribute to crystal growth on the silicon carbide single crystal substrate.
Preferably, sectional area of an inflow port of the crucible through which the mixture gas is introduced is set larger than that of an outflow port of the crucible from which the mixture gas is exhausted.
Preferably, a protruding portion having a communicating path that communicates an inlet conduit for introducing the mixture gas into the crucible to a growth room in the crucible, is provide to the crucible so as to protrude to the silicon carbide single crystal. Sectional area of the communicating path at a side where the introducing conduit is disposed is set to be small with respect to sectional area of the communicating path at a side where the growth room is disposed.
Thus, flow rate of the mixture gas at the vicinity of the silicon carbide single crystal substrate can be slowed down. Therefore, the mixture gas can be remained at the vicinity of the silicon carbide single crystal substrate for long time. Therefore, a lot of components in the mixture gas can contribute to crystal growth on the silicon carbide single crystal substrate.
Preferably, sectional area of the communicating path is gradually increased from the introducing conduit to the growth room.
Preferably, the silicon carbide single crystal substrate is fixed on a surface of a substrate fixing pedestal while gas is provided to an opposite surface of the pedestal.